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## org.apache.catalina.servlets
Class CGIServlet

    java.lang.Object
      javax.servlet.GenericServlet
          javax.servlet.http.HttpServlet
              org.apache.catalina.servlets.CGIServlet

All Implemented Interfaces:
  java.io.Serializable, javax.servlet.Servlet, javax.servlet.ServletConfig

public final class CGIServlet
extends javax.servlet.http.HttpServlet

CGI-invoking servlet for web applications, used to execute scripts which comply to the Common Gateway Interface (CGI) specification and are named in the path-info used to invoke this servlet.

Note: This code compiles and even works for simple CGI cases. Exhaustive testing has not been done. Please consider it beta quality. Feedback is appreciated to the author (see below).

Example:
If an instance of this servlet was mapped (using `<web-app>/WEB-INF/web.xml`) to:

`<web-app>/cgi-bin/*`

then the following request:

`http://localhost:8080/<web-app>/cgi-bin/dir1/script/pathinfo1`

would result in the execution of the script

`<web-app-root>/WEB-INF/cgi/dir1/script`

with the script's `PATH_INFO` set to `/pathinfo1`.

Recommendation: House all your CGI scripts under `<webapp>/WEB-INF/cgi`. This will ensure that you do not accidentally expose your cgi scripts' code to the outside world and that your cgis will be cleanly ensconced underneath the WEB-INF (i.e., non-content) area.

The default CGI location is mentioned above. You have the flexibility to put CGIs wherever you want, however:

The CGI search path will start at webAppRootDir + File.separator + cgiPathPrefix (or webAppRootDir alone if cgiPathPrefix is null).

cgiPathPrefix is defined by setting this servlet's cgiPathPrefix init parameter

CGI Specification:
derived from http://cgi-spec.golux.com. A work-in-progress & expired Internet Draft. Note no actual RFC describing the CGI specification exists. Where the behavior of this servlet differs from the specification cited above, it is either documented here, a bug, or an instance where the specification cited differs from Best Community Practice (BCP). Such instances should be well-documented here. Please email the Jakarta Tomcat group [tomcat-dev@jakarta.apache.org] with amendments.

Canonical metavariables:
The CGI specification defines the following canonical metavariables:
[excerpt from CGI specification]

      AUTH_TYPE
      CONTENT_LENGTH
      CONTENT_TYPE
      GATEWAY_INTERFACE
      PATH_INFO
      PATH_TRANSLATED
      QUERY_STRING
      REMOTE_ADDR
      REMOTE_HOST
      REMOTE_IDENT
      REMOTE_USER
      REQUEST_METHOD
      SCRIPT_NAME
      SERVER_NAME
      SERVER_PORT
      SERVER_PROTOCOL
      SERVER_SOFTWARE

Metavariables with names beginning with the protocol name (e.g., "HTTP_ACCEPT") are also canonical in their description of request header fields. The number and meaning of these fields may change independently of this specification. (See also section 6.1.5 [of the CGI specification].)

[end excerpt]

## Implementation notes

standard input handling: If your script accepts standard input, then the client must start sending input within a certain timeout period, otherwise the servlet will assume no input is coming and carry on running the script. The script's the standard input will be closed and handling of any further input from the client is undefined. Most likely it will be ignored. If this behavior becomes undesirable, then this servlet needs to be enhanced to handle threading of the spawned process' stdin, stdout, and stderr (which should not be too hard).
If you find your cgi scripts are timing out receiving input, you can set the init parameter `` of your webapps' cgi-handling servlet to be

Metavariable Values: According to the CGI specificion, implementations may choose to represent both null or missing values in an implementation-specific manner, but must define that manner. This implementation chooses to always define all required metavariables, but set the value to "" for all metavariables whose value is either null or undefined. PATH_TRANSLATED is the sole exception to this rule, as per the CGI Specification.

NPH -- Non-parsed-header implementation: This implementation does not support the CGI NPH concept, whereby server ensures that the data supplied to the script are preceisely as supplied by the client and unaltered by the server.

The function of a servlet container (including Tomcat) is specifically designed to parse and possible alter CGI-specific variables, and as such makes NPH functionality difficult to support.

The CGI specification states that compliant servers MAY support NPH output. It does not state servers MUST support NPH output to be unconditionally compliant. Thus, this implementation maintains unconditional compliance with the specification though NPH support is not present.

The CGI specification is located at http://cgi-spec.golux.com.

### TODO:

- Support for setting headers (for example, Location headers don't work)
- Support for collapsing multiple header lines (per RFC 2616)
- Ensure handling of POST method does not interfere with 2.3 Filters
- Refactor some debug code out of core
- Ensure header handling preserves encoding
- Possibly rewrite CGIRunner.run()?
- Possibly refactor CGIRunner and CGIEnvironment as non-inner classes?
- Document handling of cgi stdin when there is no stdin
- Revisit IOException handling in CGIRunner.run()
- Better documentation
- Confirm use of ServletInputStream.available() in CGIRunner.run() is not needed
- Make checking for "." and ".." in servlet & cgi PATH_INFO less draconian
- [add more to this TODO list]

Since:
  Tomcat 4.0
Version:
  $Revision: 1.22 $, $Date: 2004/06/16 18:22:20 $
Author:
  Martin T Dengler [root@martindengler.com], Amy Roh
See Also:
  Serialized Form

Nested Class Summary
`protected class` | `CGIServlet.CGIEnvironment` Encapsulates the CGI environment and rules to derive that environment from the servlet container and request information.
`protected class` | `CGIServlet.CGIRunner` Encapsulates the knowledge of how to run a CGI script, given the script's desired environment and (optionally) input/output streams
`protected class` | `CGIServlet.HTTPHeaderInputStream` This is an input stream specifically for reading HTTP headers.
`protected class` | `CGIServlet.NameValuePair` This is a simple class for storing name-value pairs.

Constructor Summary
`CGIServlet()`

Method Summary
`protected void` | `doGet(javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse res)` Provides CGI Gateway service
`protected void` | `doPost(javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse res)` Provides CGI Gateway service -- delegates to `doGet`
`void` | `init(javax.servlet.ServletConfig config)` Sets instance variables.
`static void` | `main(java.lang.String[] args)` For future testing use only; does nothing right now
`protected void` | `printServletEnvironment(javax.servlet.ServletOutputStream out, javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse res)` Prints out important Servlet API and container information

Methods inherited from class javax.servlet.http.HttpServlet
`doDelete, doHead, doOptions, doPut, doTrace, getLastModified, service, service`

Methods inherited from class javax.servlet.GenericServlet
`destroy, getInitParameter, getInitParameterNames, getServletConfig, getServletContext, getServletInfo, getServletName, init, log, log`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### CGIServlet

    public CGIServlet()

Method Detail

### init

    public void init(javax.servlet.ServletConfig config)
              throws javax.servlet.ServletException

  Sets instance variables.

  Modified from Craig R. McClanahan's InvokerServlet

  Parameters:
    `config` - a `ServletConfig` object containing the servlet's configuration and initialization parameters
  Throws:
    `javax.servlet.ServletException` - if an exception has occurred that interferes with the servlet's normal operation

### printServletEnvironment

    protected void printServletEnvironment(javax.servlet.ServletOutputStream out,
                                           javax.servlet.http.HttpServletRequest req,
                                           javax.servlet.http.HttpServletResponse res)
                                    throws java.io.IOException

  Prints out important Servlet API and container information

  Copied from SnoopAllServlet by Craig R. McClanahan

  Parameters:
    `out` - ServletOutputStream as target of the information
    `req` - HttpServletRequest object used as source of information
    `res` - HttpServletResponse object currently not used but could provide future information
  Throws:
    `java.io.IOException` - if a write operation exception occurs

### doPost

    protected void doPost(javax.servlet.http.HttpServletRequest req,
                          javax.servlet.http.HttpServletResponse res)
                   throws java.io.IOException,
                          javax.servlet.ServletException

  Provides CGI Gateway service -- delegates to `doGet`

  Parameters:
    `req` - HttpServletRequest passed in by servlet container
    `res` - HttpServletResponse passed in by servlet container
  Throws:
    `javax.servlet.ServletException` - if a servlet-specific exception occurs
    `java.io.IOException` - if a read/write exception occurs
  See Also:
    `HttpServlet`

### doGet

    protected void doGet(javax.servlet.http.HttpServletRequest req,
                         javax.servlet.http.HttpServletResponse res)
                  throws javax.servlet.ServletException,
                         java.io.IOException

  Provides CGI Gateway service

  Parameters:
    `req` - HttpServletRequest passed in by servlet container
    `res` - HttpServletResponse passed in by servlet container
  Throws:
    `javax.servlet.ServletException` - if a servlet-specific exception occurs
    `java.io.IOException` - if a read/write exception occurs
  See Also:
    `HttpServlet`

### main

    public static void main(java.lang.String[] args)

  For future testing use only; does nothing right now

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